Soil stabilization



2,801,983 Patented Aug. 6, 1957 SOIL STABILIZATION James K. Dixon andRussell L. Morgan, Riverside, Conn., assignors to American CyanamidCompany, New York, N. Y., a corporation of Maine No Drawing. ApplicationMay 5, 1951, Serial No. 224,842

16 Claims. (Cl. 2604l) This invention relates to soil stabilization andmore particularly, to a method of solidifying soil so that it willremain cohered under conditions of high strain. For many years greatdifficulty has been experienced in the construction of roadways andairfields on certain types of soil, such as the various clays, whichform very fluid, gummy muds and are therefore incapable of supportingheavy weight. Similarly, sand is unsuitable for the support of heavyvehicles in many instances. In order to overcome these difficulties,portable steel mats have been used, and of course, concrete roadways andairport runways have been extensively employed. These have thedisadvantage that they require the transportation of large quantities ofheavy construction materials, sometimes at great distances and oftenwhere there are inadequate means for transportation.

It is an object of this invention to provide a means for stabilizingsoils and sands to give them suflicient rigidity and strength to supportheavy weights, i. e., motor vehicles, military equipment, aircraft, andthe like.

It is another object of the present invention to pie vent soil erosion.

A further object of the present invention is to increase markedly theviscosity of fluid muds.

Still another object of the present invention is to solidify soil.

It is still a further object of the present invention to impartrubber-like properties to soils.

These and other objects are attained by incorporating in the soil orsand to be stabilized a water-soluble or water-dispersible polymerizablecomposition containing an aciylamido derivative, which composition iscapable of being converted to a water-insoluble state while inassociation with the soil or sand.

The following examples in which the proportions are given in parts byweight are merely illustrative. It is not intended that the scope of theinvention be limited to the details therein set forth.

Example 1 500 parts of montrnorillonite clay 50 parts of methylolacrylamide 2 parts of ammonium persulfate 0.5 part of sodium thiosulfate225 parts of water A solution of the methylol acrylamide, the ammoniumpersulfate and the sodium thiosulfate in the water is made acid withsulfuric acid to a pH of about 4 and then mixed with the clay. Theresulting mixture is spread on the ground from which the clay was takenin a layer of about 4-8 inches thick. After about 12 hours attemperatures of about 25 degrees C., a rigid hard surface is obtained.

Example 2 500 parts of kaolinite 50 parts of methylol acrylamide 50parts of acrylamide 2 parts of ammonium persulfate 0.5 part of sodiumbisulfite 300 parts of water A solution of the methylol acrylamide,acrylamide, ammonium persulfate and sodium bisultite in the water isacidified to a pH of about 3.5 with sulfuric acid and then mixed withthe clay. A layer of the mixture about 4-l0 inches thick is spread onthe soil surface from which the kaolinite was taken and after about 12hours at about 25 degrees C., a hard, rigid surface is obtained. Inthick sections very heavy vehicles may be readily supported.

Example 3 1000 parts of montmorillonite clay 25 parts of acrylamide 25parts of methylol acrylamide 25 parts of partially polymerizedmethylolacrylamide 25 parts of calcium acrylate 5 parts of ammoniumpersulfate 1 part of sodium bisulfite 600 parts of water The partiallypolymerized methylolacrylamide is prepared by polymerizingmethyloiacrylamide in aqueous solution in the presence of about 1% ofammonium persulfatc at a temperature of about 60 degrees C. until aviscous solution or dispersion results. Incorporation of this partiallypolymerized methylolacrylamide, the acrylamide, the methylolacrylamide,the calcium acrylate, the ammonium persulfate and the sodium bisufitewith the water results in the formation of a solution or dispersionwhich is made alkaline with sodium hydroxide to a pH of about 11. Thisaqueous material is mixed with the clay and the mixture then spread onthe surface from which the clay was taken and allowed to polymerize for12-24 hours at a temperature of about 20 degrees C. A tough, flexiblesurface results.

Example 4 500 parts of sand parts of methyiolacrylamide 2 parts ofammonium persulfate 0.5 part of sodium bisulfite 240 parts of water Asolution of the methylolacrylamide, ammonium persulfate and sodiumbisulfite in the water is made acid with sulfuric acid to a pH of about3.54. This is now mixed with the sand and the mixture spread in a layerabout 6 inches thick on the sub-sand surface from which the sand usedwas removed. Polymerization is allowed to take place for about l2-24hours at a temperature of about 25 degrees C. A hard, strong surface isobtained which is quite capable of supporting heavy loads.

Any polymcrizable composition containing an acrylamido derivative, whichcomposition is water-soluble or water-dispersible in the concentrationused and is at the same time capable of being converted to awater-insoluble state by polymerization processes, either of thecondensation or vinyl type or of a combination of the two, may be usedin our process to produce our new stabilized soil compositions.

The invention contemplates primarily the addition to soil of awater-soluble or water-dispersible methylol acrylamido derivative whichis methylolacrylamide, a. methylol-polyacrylamide or apoly(rnethylolacrylamide). These materials may be prepared in general inaccord-, ance with the teaching of U. S. Patent No. 2,173,005. Awater-soluble po1y(methylolacrylan1ide), for example, may be prepared asfollows:

30.4 parts of isopropanol, 364 parts of demineralized water and about 10parts of 0.1 M sulfuric acid are placed in a suitable vessel equippedwith temperature indicating means, an inert gas inlet, means foragitation and a reflux condenser, and heated to about 40 degrees C. 500parts of a 20.2% aqueous solution of methylolacrylamide are added andthe resulting solution, which has a pH of 4.7, is heated to 60 degreesC., at which point about 2 g. of potassium metabisulfite (KzSzOs) and 4g. of ammonium persulfate [(NHOzSsOs] dissolved in 100 parts of waterare added. Polymerization is permitted to continue for 1 hour whilemaintaining the temperature between about 60 degrees65 degrees C. Thepolymer solution is then cooled rapidly and adjusted to a pH of 8.5 with26 parts of 10% aqueous sodium hydroxide.

Mixtures of these methylol acrylamide derivatives may also be used, cf.Example 3, as well as mixtures of one or more of them with no more than50% of other watersoluble or water-dispersible acrylic compounds containing no methylol substitution such as acrylamide, N-alkylacrylamideswherein the alkyl group contains up to 4 carbon atoms such asN-t-butylacrylamide, methacrylamide, acrylonitrile, methacrylonitrile,acrylic acid, methacrylic acid, salts of either of these acids, i. e.,calcium acrylate. alkyl esters of either of these acids, i. e., methylmethacrylate, hydroxyethyl acrylate, and the like, cf. Examples 2 and 3.Minor amounts i. e., less than 50%, of other monovinylidene compoundssuch as vinyl acetate, vinyl chloride, vinyl pyridine, styrene,substituted styrenes, for example, the monoand di-chlorostyrenes, theaminostyrenes, o-, mand pmethyl styrenes,

alpha, para-dimethylstyrene, 2,4-dimethylstyrene, etc., monoallylphthalate, methyl vinyl ketone, allyl amine, allyl alcohol, and the likemay also be used in conjunction with the methylol acrylamidoderivatives. In selecting any particular unmethylolated monovinylidenecompound, or in determining the relative proportions of methylolacrylamide derivative and selected unmethylolated monovinylidenecompound to be used, it must be borne in mind that the mixture should bewater-soluble or water-dispersible so that it may be readily applied tothe soil to be stabilized.

While we do not wish to be limited to any particular theory, we believethat soil or sand treated with polymerizable methylolacrylamidoderivatives according to the process of the present invention isstabilized because it contains polymeric material which is cross-linkedby reason of having undergone two distinct types of polymerization, i.e., polymerization of the vinyl groups and condensation of the methylolgroups, and is therefore water-insoluble. that a soil-polyacrylamidemixture readily disintegrates in the presence of water becausepolyacrylamide, being essentially a linear polymer, is soluble in water.If acrylamide, however, or any other unmethylolated monoacrylamidoderivative such as, for example, N-t-butylacrylamide, is copolymerizedwith a polymerizable monovinylidene compound of the type listed above assuitable for copolymerization with the methylol acrylamido derivatives,so selected that the polymerizable mixture is water-soluble orwater-dispersible and the polymerized product is water-insoluble, suchcopolymerizable compositions are useful in our process. Thus, forexample, copolymers of acrylamide with calcium acrylate are particularlyuseful. Acrylamide may also be used by aftertreating soil containingpolyacrylamide with formaldehyde whereby the soil-resin mixture becomesnot disintegrable by water.

The present invention is intended to cover only suitable polymers andcopolymers of the methylol acrylamido derivatives, and copolymers withmonovinylidene compounds of acrylamido derivatives either methylolatedor not. The use for soil stabilization of certain copolymers of acrylicacid derivatives, including the acrylamido and methylolacrylamidoderivatives, with polyvinyl compounds is described and claimed in thecopending ap- This theory is substantiated by the fact til) 4 plicationof one of the present inventors, Russell L. Morgan, with John J.Padbury, Serial No. 236,454, filed July 12, 1951, entitled SoilStabilization, now abancloned.

Polymerization of the vinyl groups of the compounds used in accordancewith our invention is effected preferably with any of the usualwater-soluble oxygen-containing catalysts, such as the ammonium,potassium and sodium persulfates, hydrogen peroxide, the alkali metaland ammonium chlorates and the like. It is generally desirable to use aredox catalyst system of an oxygencontaining compound with a reducingagent, such as sodium thiosulfate, sodium or potassium bisulfite, etc.,a typical combination being the chloric acid-bisulfite system describedin the copending application of Arthur Cresswell, Serial No. 208,797,filed February 1, 1951, now abandoned. We are not limited to anyparticular quantity of catalyst but in general from about 0.1% to about10%, based on the weight of polymerizable monomers may be used.

In order that the methylol groups of the compounds used be polymerizedin relatively short periods of time, it is desirable that the solutionsbe either strongly alkaline or strongly acidic. Certain redox systems(e. g. chloric acid-bisulfite) require acid conditions, and othersoperate but under acid conditions. Hence, polymerization below pH 7 ispreferred. If acid polymerization is contemplated, any desired acidicmaterial including sulfuric acid, hydrochloric acid, phosphoric acid,diammonium hydrogen phosphate, ammonium chloride, ammonium sulfate,etc., may be used for this purpose. In some cases, it may be desirableto use organic acids but since they are more expensive, this isgenerally not an economical procedure. However, acetic acid, oxalicacid, tartaric acid, phthalic anhydride and other acids may be used.

While the quantities of acid employed may be varied widely from verysmall amounts, which will merely produce an acid reaction, it isgenerally preferable that the pH be relatively low and of the order of3.5-4.

In some cases, particularly with soils containing acidadsorbing orreacting materials, it may be more desirable to polymerize the methylolgroups under alkaline conditions. For such purposes any water-solublealkali may be used, but in general, sodium carbonate, sodium hydroxide,ammonium hydroxide, potassium hydroxide and calcium hydroxide arepreferred because they are relatively inexpensive as compared to otheralkaline materials. Organic bases such as guanidine carbonate, however,may be used.

When alkaline materials are used to catalyze the polymerization of themethylol groups, it is preferable that the pH be relatively high, of theorder of about 11, but if it is not necessary to polymerize the methylolgroups rapidly, lower degrees of alkalinity, ranging all the way down toneutrality, may be used.

In the case of alkaline soils it is possible to use a catalyst systemcomprising an amine or the activator for the vinyl polymerization.Examples of activators for peroxy type catalysts such as persulfates arepolyamines, i. e., diethylene triamine tetraethylene pentamine, etc.,triethanolamine, dimethylaminopropionitrile, dimethylaminoacetonitrile,etc.

The gel formation of a particular resin may vary depending upon whetherpolymerization is elfected in the presence of acid or alkali, and thisfactor should also be considered in determining the polymerizationconditions. If, for example, the methylol groups of methylolacrylamideare made to condense under alkaline conditions, a more flexible, toughergel is obtained than when condensation takes place in the presence ofacid. Under at least some circumstances, therefore, alkalinecondensation of methylolacrylamide is to be preferred.

Our invention is applicable to all types of clays and sands and varioussoils containing mixtures of such materials which are normally soft ormuddy, and which would ordinarily not be satisfactory for use by heavyvehicles.

The ratio of poiymerizablc material to soil may be varied widely, butgenerally should be within the range of about 3-15 parts by weight ofsoil to 1 part by Weight of polymerizable material. Ordinarily, thepolymerizable material is dissolved or dispersed in water to form asolution or dispersion which is mixed with the soil. The concentrationof the solution or dispersion and the quantity used should be regulatedso that the concentration of water in the final mixture of soil andstabilizing additive is between about and 70% by weight, and preferablyabout or 60%. The proportion of water used determines to some extent theproperties of the resulting stabilized soil.

The polymcrizable material may be incorporated with the soil in anydesired manner as, for example, by mixing in a revolving drum. Anothermethod of application which may sometimes be employed is spraying anaqueous solution or dispersion of the polymerizable material onto theground which it is desired to toughen. This expedient may not result insufficient penetration for some purposes, however, although thedifiiculty can often be at least partially overcome by plowing the soileither before or after spraying or simultaneously therewith. This canconveniently be done with the roto tiller type of plow having revolvingtynes which thoroughly mix the top few inches of soil.

In order to ensure sufilcient strengthening of any given section ofground for the support of heavy weight, a surface of from about 4-12inches of soil treated according to the process of the present inventionshould be provided. The actual depth necessary will, 5 course, varydepending upon how fluid the soil is to begin with or, in other Words,how much solidifying is required.

As used in the present specification and claims the term stabilize asapplied to soil means to impart to the soil high viscosity, solid orrubber-like properties. Moreover, the expression water-soluble as usedis intended to be inclusive of the expression water-dispersible.

We claim;

1. A process for treating soil which comprises incorporating apolymerizable water-dispersible material substantially free ofalkylidcne bisacrylamides and of the group consisting of methylolacrylamide, methylol polyacrylamide and polymethylol acrylamide intosoil and polymerizing the polymerizable matter in the resultingcomposition in the presence of an oxygen-containing polymerizationcatalyst at naturally occurring temperatures to a substantiallywater-insoluble state in contact with natural soil substantially withinthe surface of the earth in the presence of water.

2. A process according to claim 1 in which said material is polymethylolacrylamide.

3. A process according to claim 1 in which said material derivative isadmixed with a water-dispersible copolymerizable vinylidene monomer.

4. A process according to claim 1 in which said material derivative ismethylol acrylamide and is admixed with a compound of the groupconsisting of acrylic acid, methacrylic acid and salts of said acids.

5. A process according to claim 1 in which 1 part by weight ofpolymerizable material is incorporated into at least 3 parts by weightof soil.

6. A process for treating soil which comprises incorporating 1 part byweight of a polymerizable water dispersible material substantially freeof alkylidene bisacrylamides and containing a major proportion of anacrylamido derivative of the group consisting of methylol acrylamidc,methylol polyacrylamide, and polymethylol acrylamide and a minorproportion of a compound of the group consisting of acrylic acid,moth-acrylic acid and salts of said acids into at least 3 parts byweight of soil and polymerizing the polymerizahle matter in theresulting composition at naturally occurring temperatures to asubstantially water-insoluble state in contact with natural soilsubstantially within the surface of the earth in the presence of anaqueous solution of an oxygen-containing polymerization catalyst.

7. A process according to claim 6 in which said compound is calciumacrylate.

8. A process according to claim 6 in which said acrylarnido derivativeis methylol acrylamide.

9. A process according to claim 6 in which said acrylamido derivative ismethylol acrylamide and said compound is calcium acrylate.

10. A process according to claim 6 in which a quantity of soil isremoved from the ground, mixed with water along with said catalyst andsaid polymerizable material, the resulting mixture deposited in the sameapproximate ground location from which the soil was removed and themixture polymerized in situ.

ll. An earthen mass which comprises a soil-polymer composition preparedaccording to the process of claim 1.

12. An earthen mass which comprises a soil-polymer composition preparedaccording to the process of claim 6.

13. An earthen mass which comprises a soil-polymer composition preparedaccording to the process of claim 9.

14. A process according to claim 1 in which said material is methylolpolyacrylarnide.

15. A process according to claim 1 in which said material is methylolacrylamide.

16. A process for treating soil which comprises incorporating apolymerizable watcr'dispersible material substantially free ofaiitylidcne bisacrylamides and of the group consisting of methylolacrylamidc, methylol polyacrylamide and polymelhylol acrylamide intosoil and converting the resulting composition to a substantiallywater-insoluble state in contact with natural soil substantially withinthe surface of the earth in the presence of water, an oxygen-containingpolymerization catalyst and polymerizing the polymeriznble matter insaid composition without the application of artificial heat.

References Cited in the file of this patent UNITED STATES PATENTS2,069,376 Madsen Feb. 2, 1937 2,173,005 Strain Sept. 12, 1939 2,401,348Hauser et a1. June 4, 1946 2,598,663 Kropa June 3, 1952 2,614,998 LeaOct. 21, 1952 2,616,818 Azorlosa Nov. 4, 1952 2,625,529 HedriCl-i et al.Jan. 13, 1953 FOREIGN PATENTS 482,897 Great Britain Apr. 7, 1938 501,726Belgium Mar. 7, 1951

1. A PROCESS FOR TREATING SOIL WHICH COMPRISES INCORPORATING APOLYMERIZABLE WATER-DISPERSIBLE MATERIAL SUBSTANTIALLY FREE OFALKYLIDENE BISACRYLAMIDES AND OF THE GROUP CONSISTING OF METHYLOLACRYLAMIDE, METHYLOL POLYACRYLAMIDE AND POLYMETHYLOL ACRYLAMIDE INTOSOIL AND POLYMERIZING THE POLYMERIZABLE MATER IN THE RESULTINGCOMPOSITION IN THE PRESENCE OF AN OXYGEN-CONTAINING POLYMERIZATIONCATALYST AT NATURALLY OCCURRING TEMPERATURES TO A SUBSTANTIALLYWATER-INSOLUBLE STATE IN CONTACT WITH NATURAL SOIL SUBSTANTIALLY WITHINTHE SURFACE OF THE EARTH IN THE PRESENCE OF WATER.